Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-07-13
2002-12-03
Pham, Chi (Department: 2731)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S343000
Reexamination Certificate
active
06490316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a correlation detection apparatus used in detecting the correlation of a spread spectrum signal in a CDMA (Code Division Multiple Access) radio communication apparatus, and more particularly, to a correlation detection apparatus applicable to a digital matched filter.
2. Related Art
A matched filter is used at a receiving station to demodulate a spread spectrum signal that is generated by multiplying transmission data with a spreading code at a transmitting station.
FIG. 1
illustrates an example of a configuration of a conventional matched filter. The matched filter illustrated in
FIG. 1
is a digital matched filter with
4
taps for spreading ratio
4
composed of FIR digital filters.
Digital signal IO is input to signal input terminal
1
of the digital matched filter. Digital signal IO is, for example, a digital signal generated by sampling a spread spectrum signal at a sampling frequency of 4,096 MHz. This digital signal IO is input to first flip-flop group
11
of shift register with taps
10
(hereinafter referred to as shift register
10
), and then shifted sequentially to fourth flip-flop group
14
from first flip-flop group
11
in synchronization with clock CLK of 4,096 MHz input to clock input terminal
2
.
Output Signals output from every tap and the flip-flop at the last stage of shift register
10
are respectively input to first to fourth multipliers
15
to
18
. Corresponding despreading code C among from despreading code sequence C
3
C
2
C
1
C
0
is provided to each of first to fourth multipliers
15
to
18
. Accordingly, first multiplier
15
executes multiplication of an output signal from first flip-flop group
11
by despreading code Co (1 bit). Similarly, second to fourth multipliers
16
to
18
execute respectively multiplication of output signals from second to fourth flip-flop groups
12
to
14
respectively by despreading codes C
1
to C
3
. First to fourth multiplies
15
to
18
respectively execute multiplication of respective output signals from first to fourth flip-flop groups by 1 when the despreading code indicates 0, and multiplication of output signals from first to fourth flip-flop groups by −1 when the despreading code indicates 1.
First adder
19
adds outputs from first and second multipliers
15
and
16
, second adder
20
adds outputs from third and fourth adders
17
and
18
, and third multipliers
21
adds outputs from first and second adders
19
and
20
. As a result, correlation value MFOUT of digital signal IO with despreading code sequence C
3
C
2
C
1
C
0
is output to external through output terminal
3
.
Conventionally, the digital matched filter described above rewrites despreading code sequence C
3
C
2
C
1
C
0
on a basis of one symbol period to detect the correlation of each symbol. As a result, it is not possible to detect the correlation of delayed waves input after one symbol period passes.
Such a condition has remained the inconveniences that it is not possible to effectively utilize delayed waves input after one symbol period passes in the CDMA system that enables a plurality of delayed waves to be utilized. One of means of solving the inconveniences suggests a configuration having a plurality of parallel connected matched filters each of which is illustrated in FIG.
1
.
FIG. 2
illustrates the configuration having a plurality of parallel connected matched filters each of which is illustrated in FIG.
1
. First to fourth digital matched filters M
1
to M
4
are provided in parallel.
However, the configuration with the plurality of parallel connected matched filters results in the problem that a circuit scale and power consumption are increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a correlation detection apparatus capable of detecting the correlation of delayed waves arriving after one symbol period passes, and of decreasing a circuit scale and power consumption.
The correlation detection apparatus has a data storage section for storing symbol data, a plurality of correlation calculators connected to the data storage section in parallel, each for executing the correlation detection of the symbol data with a spreading code for despreading, and a code controller for rewriting the spreading code for each of the correlation calculators on a basis of a plurality of symbol periods individually.
According to the configuration, a plurality of correlation calculators are connected to the data storage section in parallel, and the spreading codes in respective correlation calculators are individually rewritten after a period corresponding to a plurality of symbols passes. Therefore, it is possible to detect the correlation of delayed waves arriving after one symbol period passes, and to decrease a circuit scale and power consumption largely compared with the case of arranging a plurality of digital matched filters in parallel to perform the processing.
REFERENCES:
patent: 6064690 (2000-05-01), Zhou et al.
patent: 6069915 (2000-05-01), Hulbert
patent: 6393046 (2002-05-01), Kohli et al.
patent: 6-235762 (1994-08-01), None
patent: 9-55685 (1997-02-01), None
patent: 9-247044 (1997-09-01), None
patent: 9-321660 (1997-12-01), None
patent: 10-173485 (1998-06-01), None
patent: 10-178334 (1998-06-01), None
patent: 10-178368 (1998-06-01), None
English Language Abstract of JP 6-235762.
English Language Abstract of JP 10-173485.
English Language Abstract of JP 10-178368.
English Language Abstract of JP 10-178334.
English Language Abstract of JP 9-247044.
English Language Abstract of JP 9-55685.
English Language Abstract of JP 9-321660.
Motegi Isao
Shinde Hiroki
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Pham Chi
Tran Khai
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